1. Field of the Invention
The present invention relates to an exposure apparatus used in a semiconductor fabrication process.
2. Description of the Related Art
In general, a lithographic process in semiconductor device fabrication includes five steps, i.e., a surface treatment step, a resist applying step, an exposure step, a developing step, and an etching step. Vacuum apparatuses such as a projection exposure apparatus and an etching apparatus are used to perform these steps. These vacuum apparatuses include mechanisms for clamping wafers by means of members. The wafers are transported by the mechanical structures or fixed on stages.
When a post-treatment of the resist applying step is insufficient, resist is left on an edge of each semiconductor wafer. In this case, when the wafer is clamped by the mechanism, the residual resist peels from the wafer upon contact between the resist and clamp members. The peeling resist becomes a foreign object such as dust, thus degrading the degree of cleanliness in the clean room.
Side rinse techniques are available as a means of preventing production of foreign objects (dust), as disclosed in Published Examined Japanese Patent Application No. 53-37706, Published Unexamined Japanese Patent Applications Nos. 55-12750, 58-58731, and 58-191434, Published Unexamined Utility Model Applications Nos. 60-94660 and 61-111151, and Published Unexamined Japanese Patent Applications Nos. 61-121333 and 61-184824.
Lower-surface washing techniques are also available as a means of preventing production of foreign objects (dust), as disclosed in Published Unexamined Japanese Patent Application No. 58-200537, Published Unexamined Utility Model Applications Nos. 58-81932 and 59-67930, and Published Unexamined Japanese Patent Applications Nos. 60-110118, 60-121719, 60-189937, and 61-239625.
In each conventional resist removal technique described above, resist is removed while a wafer is being rotated. For this reason, the resist tends to be left at a portion of an orientation flat (O.F.) of the wafer and may peel therefrom. When the resist removal range is so increased as to solve the above problem, the number of semiconductor devices per wafer is decreased, and consequently product yield also decreases. Even when another conventional apparatus is used wherein a resist projects upwards at the boundary of the resist removal area and a resist non-removal area, and a plurality of points outside the exposure area are used as focusing targets, the drawback of defocusing occurs at the point where the resist projects upwards.
Techniques for solving the above problem, which provide the O.F. with the same treatment as the curved edge are disclosed in Published Unexamined Japanese Patent Application Nos. 59-117123 and 61-219135. According to such a technique, a porous member containing a solvent is brought into contact with the wafer edge to remove the resist.
Even using this technique, however, problems such as defocusing during exposure are not solved.
For the purpose of eliminating the defocusing problem during exposure, exposure techniques for circularly eliminating the resist layer from the wafer edge are disclosed in Published Unexamined Japanese Patent Application Nos. 58-159535 and 61-73330, and Published Unexamined Utility Model Application No. 60-94661.
According to this technique, a semiconductor wafer is chucked by a chuck having a rotating shaft mounted with a cam having the same outline as that of the semiconductor wafer. An exposure light beam guided through an optical fiber is emitted along the edge of the cam while the wafer is being rotated, thereby exposing the edge portion of the wafer.
However, in the exposure apparatus having the cam described above, the cam must be replaced with another in accordance with types of wafers, resulting in inconvenience and preventing full-automation (FA) of the exposure step. In addition, the cam wears down, producing dust.
In the above exposure technique, in order to prevent the resist from peeling from wafer portions in contact with a mechanical arm during semiconductor wafer transportation, the resist is removed from these wafer contact portions in advance. According to this technique, since the resist is removed by exposing the entire edge portion of the wafer which includes the above wafer contact portions, the resist is excessively removed from the wafer edge portions which are not brought into contact with the mechanical arm.
In the above exposure technique, an ultraviolet ray is guided onto a wafer through an optical fiber and is moved across the wafer. Vibrations from the drive system are transmitted to the fiber, and a sharp exposure image cannot be obtained.
A read method using a CCD line sensor has a low throughput at present.
In addition, since the adjustment range of exposure amount per unit time is narrow, resist bubbles may be formed.